November 2013

Conference coverage: 3rd PFP research retreat

The third International Patellofemoral Pain Research Retreat picked up where previous retreats had left off in examining proximal and distal factors related to PFP and subgroups of patients who might respond to targeted interventions. But this retreat broke some new ground as well.

By Jordana Bieze Foster

A successful research retreat doesn’t just summarize and analyze current research, its conclusions also direct and inspire future studies. That model seems to be succeeding in the patellofemoral pain (PFP) research community, as evidenced by presentations at the third International Patellofemoral Pain Research Retreat of studies that evolved from the previous two PFP retreats.

The third PFP research retreat, held in September in Vancouver, BC, featured a number of studies that further explored those two themes, including several whose origins could be traced directly to discussions from previous retreats. But the Vancouver event also broke some new ground with a provocative keynote speaker and two oral research presentations that challenged PFP researchers to revisit conventional thinking about pain and its origins (see sidebar, page 20). The full proceedings of the event, along with a consensus statement, will be published in a future issue of the British Journal of Sports Medicine.

Distal and proximal factors

Increasingly, researchers are confirming that biomechanical factors at the foot and ankle, trunk and hip, or some combination of distal and proximal joints are associated with patellofemoral pain—which is consistent with the anecdotal reports of clinicians who have had success treating PFP with such interventions as foot orthoses, hip strengthening, or gait retraining that encourages runners to “squeeze the buns.”

“Some of the problems manifesting in the hip in these patients may be the result of something that’s happening in the foot, for example, so you have to look at the whole patient,” said Jenny McConnell, BAppSc(Phty), GradDipManTher, MBiomedEng, a physiotherapist in Sydney, Australia, who is best known for the musculoskeletal taping technique that bears her name.

Most studies have focused on either proximal or distal factors, but research from the University of North Carolina at Chapel Hill presented in Vancouver found that both decreased ankle dorsiflexion range of motion (ROM) during knee extension and decreased hip abduction strength were significantly correlated with increased knee abduction in one group of 19 women with PFP.1

“Both distal and proximal structures are associated with knee abduction angle in individuals with patellofemoral pain, which indicates that comprehensive assessment is necessary when we treat these patients,” said Shiho Goto, ATC, a doctoral research assistant at UNC-Chapel Hill, who presented the findings in Vancouver.

Goto noted, however, that those two variables accounted for only 41% of the variability in frontal plane knee mechanics during a single leg squat, suggesting that other factors are likely involved and that different subgroups of patients with PFP may be affected by different combinations of factors.

Other studies presented in Vancouver identified other hip variables as potential risk factors for PFP. Researchers from the University of Wisconsin-La Crosse found that increased pain during stair descent was significantly correlated with neuromuscular and kinematic variables at the hip, though the specific findings contrasted with some previous research.2 Researchers from the University of Southern California in Los Angeles found that hip extensor strength was associated with patellofemoral joint stress during running in 20 healthy women, and that hip extensor weakness was also related to a more upright trunk flexion angle.3

The latter finding was consistent with a North American multicenter study of 46 patients with PFP and 31 controls that found that female participants with PFP had significantly decreased forward trunk lean (a more upright posture) during running than male or female controls.4 However, the same authors found that pelvic and trunk kinematics did not correlate significantly with intensity of pain as measured on a visual analog scale.5 Similarly perplexing were the findings of a study from Brazil, in which ipsilateral trunk lean was correlated with knee abduction in 30 controls but not in 30 patients with PFP.6 The lack of correlations suggests within-group variability, which in turn supports the concept of PFP subgroups.

Interventions and inconsistencies

The research supporting the influence of distal and proximal mechanics on patellofemoral pain suggests interventions that alter those mechanics should improve pain in patients with PFP. Studies are starting to demonstrate that, but are also finding that distal and proximal interventions do not always have the expected effects.

In 16 patients with patellofemoral pain, researchers from Queen Mary University of London, UK, found that greater pronation (based on the Foot Posture Index) was moderately correlated with greater decreases in hip adduction with the use of prefabricated foot orthoses.7 Investigators from Saint Louis University in Missouri found that instructing patients with PFP to control frontal plane knee motion during a single leg squat resulted in increased trunk lean in the direction of the weight-bearing limb in addition to decreased pain.8

In a collaboration between the University of Isfahan in Iran and the University of Southern California, a posterolateral hip strengthening program and a quadriceps strengthening program both significantly improved pain and function in patients with PFP immediately after either eight-week program and six months later.9 The effects of the hip program, however, were significantly greater than those of the quadriceps program—findings that are consistent with those of a similar study by the aforementioned North American multicenter group, presented in part this summer at the annual meeting of the National Athletic Trainers Association (see “Positives for PFP: Benefits of six-week rehab are retained,” July 2013, page 15) and again in Vancouver.10

But when the multicenter group analyzed a subset of participants for whom biomechanical data had been obtained, they found that neither quadriceps nor hip/core strengthening had pronounced effects on hip or knee mechanics.11 Conversely, in a study from Laval University in Quebec City, Canada, patients with PFP who completed an eight-week multimodal rehabilitation program, which included strengthening and motor control exercises, demonstrated significant improvements in pain and function as well as significant changes in hip kinematics during some functional tasks.12 However, hip kinematics during running and lower limb muscle strength were unchanged following the program.12,13

One factor that may be influencing the results of intervention studies is that certain exercises appear to have different effects in patients with PFP than in healthy populations, according to a study from Western University of Health Sciences in Pomona, CA.14 Because the tensor fascia lata (TFL) can be overactive in patients with PFP, hip-based interventions for PFP typically aim to strengthen the gluteal muscles while limiting TFL activation. But when the Western University researchers assessed three specific exercises designed to accomplish this, they found the exercises had the expected effects in 20 pain-free controls but activated the TFL much more than expected in six patients with PFP.

“If, in these exercises that are supposed to be beneficial, patients are actually activating the TFL more than controls, I would think that for other exercises it would be even worse,” said David M. Selkowitz, PT, PhD, a professor of physical therapy education at the university, who presented his group’s findings in Vancouver.

Sussing out subgroups

The inconsistent findings regarding distal and proximal variables affecting PFP seem to support the idea—discussed at some length during both previous research retreats—that subgroups of patients with PFP likely exist, and may be differentiated with regard to the mechanism underlying the pain, the interventions to which the patient responds, and/or the degree to which various intrinsic and extrinsic factors affect the pain experience.

Evidence seems to suggest that one of those factors is gender. Two subanalyses of the Joint Undertaking to Monitor and Prevent Anterior Cruciate Ligament Injury (JUMP-ACL) database of military cadets suggest that risk factors for PFP are different in men and women;15,16 the aforementioned multicenter study group also found gender differences in the pelvic and trunk mechanics associated with PFP.4

Age may be another subgroup determinant. Researchers from Aalborg University Hospital in Denmark found a 7% prevalence of PFP in a group of 2,200 adolescents, and a prevalence 2.3 times higher in girls than boys.17 But in a study comparing a multimodal physical therapy intervention to patient education alone, the same investigators found the effectiveness of either intervention in 121 adolescents was lower than expected; 29% of patients in the education group felt they were recovered at 12 months compared to 38% of those in the physical therapy group.18 This suggests the subgroup of adolescents with PFP may require an approach to physical therapy that differs from that typically used in adults.

“I was pretty confident that we would see a large proportion of recovered adolescents, so I was surprised,” said Michael S. Rathleff, PT, a researcher in the hospital’s Orthopedic Surgery Research Unit, who presented the findings from the latter study in Vancouver. “Some people believe we shouldn’t do much for patellofemoral pain in these adolescent patients because they’ll get over it, but that really doesn’t happen.”

A number of patellofemoral pain studies thus far have produced findings that suggest the existence of subgroups, but few if any have been designed specifically to identify subgroups. In a project whose origins can be traced back to the first PFP research retreat, investigators from the University of Central Lancashire in the UK are working to address that void with a multicenter trial to confirm the existence of subgroups based on six characteristics that could be identified using routine clinical tests and could be addressed using known interventions. As it turns out, that’s easier said than done.

Data for the first 75 patients were presented at the Vancouver retreat,19 and most of those fell into three of the six subgroups: quadriceps muscle weakness (72 patients), patellar hypomobility (69), and hip muscle weakness (62). In addition, 24 patients fit in the subgroup for lower limb biarticular muscle tightness, and 25 fit in the subgroup for pronated feet. No patients had yet qualified for the sixth subgroup, patellar hypermobility.

“We need more than 75 patients to properly address the subgroups because there’s so much overlap,” said James Selfe, PhD, a professor of physiotherapy at the university, who presented the findings in Vancouver. “We’re going to go back and look at different [clinical test] cutoffs for the final analysis and see how that changes the subgroups.”

The aforementioned North American multicenter study group analyzed a subset of their data specific to the hip/core-based exercise protocol and developed a preliminary clinical prediction rule for a subgroup of men with PFP.20 Specifically, they calculated a moderate likelihood that men with PFP will benefit from this type of exercise program if they present with hip extension strength at or below 25% of body mass and anterior core endurance of 105 seconds or less.

The concept of clinical prediction rules, however, was a matter of some debate at the Vancouver retreat.

“We see such varied responses to treatment, and you can’t really say if you do A then you should expect B,” McConnell said. “The way some clinical prediction rules are being presented is really taking away from clinical reasoning.”

More than one research group has developed a clinical prediction rule for identifying a subgroup of patients with PFP who are most likely to benefit from foot orthoses.21,22

“In our randomized clinical trial,23 we saw a lot of variability with foot orthoses, so we did go to a clinical prediction rule to subgroup them,” said Natalie Collins, PhD, a physiotherapist and postdoctoral research fellow in the department of mechanical engineering at the University of Melbourne in Australia. “But it’s not being sold as a ‘rule,’ it’s just increasing the likelihood that the treatment will work.”

REFERENCES

Goto S, Padua DA. Distal and proximal structures are associated with frontal plane knee kinematics during a single-leg squat task in females with patellofemoral pain. Presented at the third International Patellofemoral Pain Research Retreat, Vancouver, BC, September 2013.

Aminaka N, Pietrosimone BG, Gribble PA. Correlation among pain, neuromuscular factors, and lower extremity kinematics in those with patellofemoral pain during stair descent. Presented at the third International Patellofemoral Pain Research Retreat, Vancouver, BC, September 2013.

Teng H-L, Powers CM. Diminished hip extensor strength is associated with a more upright trunk posture and higher patellofemoral joint stress during running. Presented at the third International Patellofemoral Pain Research Retreat, Vancouver, BC, September 2013.

Bazett-Jones DM, Earl-Boehm JE, Bolgla LA, et al. Differences among pelvic and trunk kinematics among those with and without patellofemoral pain. Presented at the third International Patellofemoral Pain Research Retreat, Vancouver, BC, September 2013.

Bazett-Jones DM, Earl-Boehm JE, Bolgla LA, et al. Relationships among pelvic and trunk kinematics, pain and strength. Presented at the third International Patellofemoral Pain Research Retreat, Vancouver, BC, September 2013.

Nakagawa TH, Maciel CD, Serrao FV. Trunk biomechanics and its association with hip and knee kinematics in people with and without patellofemoral pain. Presented at the third International Patellofemoral Pain Research Retreat, Vancouver, BC, September 2013.

Lack S, Barton C, Morrissey D. The effect of foot orthoses on hip and knee kinematics and muscle activity during a functional step-up task in individuals with patellofemoral pain. Presented at the third International Patellofemoral Pain Research Retreat, Vancouver, BC, September 2013.

Salsich GB, Graci V, Meister M. Changes in trunk and lower extremity segment kinematics following movement pattern instruction in patients with patellofemoral pain. Presented at the third International Patellofemoral Pain Research Retreat, Vancouver, BC, September 2013.

Ferber R, Bolgla L, Earl-Boehm J, et al. Proximal vs local rehabilitation for the treatment of patellofemoral pain: An outcome-based randomized controlled trial. Presented at the third International Patellofemoral Pain Research Retreat, Vancouver, BC, September 2013.

Earl-Boehm JE, Bazett-Jones D, Bolgla L, et al. Changes in lower extremity biomechanics following knee or hip focused rehabilitation in patients with PFP: an RCT study. Presented at the third International Patellofemoral Pain Research Retreat, Vancouver, BC, September 2013.

Esculier JF, Roy JS, Bouyer LJ. Comparing lower limb kinematics of runners with patellofemoral pain syndrome before and after rehabilitation to healthy controls. Presented at the third International Patellofemoral Pain Research Retreat, Vancouver, BC, September 2013.

Esculier JF, Roy JS, Bouyer LJ. Effects of strengthening, motor control exercises and training advice on symptoms of recreational runners with patellofemoral pain. Presented at the third International Patellofemoral Pain Research Retreat, Vancouver, BC, September 2013.

Selkowitz DM, Beneck GJ, Bui M, Powers CM. Differences in hip muscle activation between persons with and without PFP during common therapeutic exercises recommended for hip strengthening. Presented at the third International Patellofemoral Pain Research Retreat, Vancouver, BC, September 2013.

Boling M, Nguyen AD, Padua D, et al. Gender-specific risk factor profiles for the development of patellofemoral pain. Presented at the third International Patellofemoral Pain Research Retreat, Vancouver, BC, September 2013.

Nguyen AD, Padua D, Marshall S, et al. Kinematic and strength differences between males and females with a history of patellofemoral pain. Presented at the third International Patellofemoral Pain Research Retreat, Vancouver, BC, September 2013.

Rathleff CR, Roos EM, Olesen JL, et al. Prevalence and severity of patellofemoral pain among adolescents – a population-based study. Presented at the third International Patellofemoral Pain Research Retreat, Vancouver, BC, September 2013.

Rathleff MS, Roos EM, Olesen JL, Rasmussen S. Patient education with or without the addition of multimodal physiotherapy for adolescent patellofemoral pain – a cluster randomized study among 121 adolescents with 12 months follow-up. Presented at the third International Patellofemoral Pain Research Retreat, Vancouver, BC, September 2013.

Bolgla L, Earl-Boehm J, Emery C, et al. Development of a preliminary clinical prediction rule to identify males with patellofemoral pain likely to benefit from a core- and hip-based rehabilitation program. Presented at the third International Patellofemoral Pain Research Retreat, Vancouver, BC, September 2013.

Noehren B, Lattermann C. The association between mechanical pain threshold and hip adduction angle in patients with patellofemoral pain. Presented at the third International Patellofemoral Pain Research Retreat, Vancouver, BC, September 2013.

Rathleff MS, Roos EM, Olesen JL, et al. Self-reported recovery among adolescent females with patellofemoral pain in associated with improvement in localized hyperalgesia. Presented at the third International Patellofemoral Pain Research Retreat, Vancouver, BC, September 2013.